U.S. patent application number 10/427845 was filed with the patent office on 2004-01-22 for dynamic tilt limiter for fluid dynamic bearings.
Invention is credited to Ameen, Mohammad Mahbubul, Khan, Raquib Uddin, Kloeppel, Klaus.
Application Number | 20040012287 10/427845 |
Document ID | / |
Family ID | 30448517 |
Filed Date | 2004-01-22 |
United States Patent
Application |
20040012287 |
Kind Code |
A1 |
Kloeppel, Klaus ; et
al. |
January 22, 2004 |
Dynamic tilt limiter for fluid dynamic bearings
Abstract
A disc drive data storage system includes a hydrodynamic bearing
comprising a housing having a central axis, a stationary member
that is fixed with respect to the housing and coaxial with the
central axis, and a rotatable member that is rotatable about the
central axis with respect to the stationary member. A hydrodynamic
bearing interconnects the stationary member and the rotatable
member. At least a portion of a surface of one or more of the
hydrodynamic bearing components has a tilt-limiting layer formed
thereon to restrict the tilting distance between the working
surfaces in the disc drive data storage system.
Inventors: |
Kloeppel, Klaus;
(Watsonville, CA) ; Ameen, Mohammad Mahbubul;
(Campbell, CA) ; Khan, Raquib Uddin; (Pleasanton,
CA) |
Correspondence
Address: |
MOSER, PATTERSON & SHERIDAN, L.L.P.
595 SHREWSBURY AVENUE
SUITE 100
SHREWSBURY
NJ
07702
US
|
Family ID: |
30448517 |
Appl. No.: |
10/427845 |
Filed: |
May 1, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60396760 |
Jul 17, 2002 |
|
|
|
Current U.S.
Class: |
310/90 |
Current CPC
Class: |
H02K 7/085 20130101 |
Class at
Publication: |
310/90 |
International
Class: |
H02K 007/08 |
Claims
1. A disc drive storage system, comprising: a housing having a
central axis; a stationary member that is fixed with respect to the
housing and coaxial with the central axis; a stator fixed with
respect to the housing; a rotatable member that is rotatable about
the central axis with respect to the stationary member; a rotor
supported by the rotatable member and magnetically coupled to the
stator; at least one data storage disc attached to and coaxial with
the rotatable member; an actuator supporting a head proximate to
the data storage disc for communicating with the disc; and a
hydrodynamic bearing interconnecting the stationary member and the
rotatable member, the bearing having at least a portion of one
working surface comprising a tilt-limiting layer.
2. The disc drive storage system of claim 1 wherein the
tilt-limiting layer comprises a material that improves the hardness
of the working surface of the bearing.
3. The disc drive storage system of claim 1 wherein the
tilt-limiting layer reduces the coefficient of friction of the
working surface of the bearing.
4. The disc drive storage system of claim 1 wherein the
tilt-limiting layer comprises a material selected from the group
consisting of diamond-like-carbon, hydrogenated
diamond-like-carbon, nitrogenated diamond-like-carbon, nickel
phosphide (NiP), nickel boride (NiB), and combinations thereof.
5. The disc drive storage system of claim 1 wherein the
tilt-limiting layer has a thickness sufficient to limit tilting
between the working surfaces of the bearing.
6. The disc drive storage system of claim 1 wherein the
tilt-limiting layer is formed on an adhesive layer.
7. The disc drive storage system of claim 7 wherein the adhesive
layer comprises one or more material selected from the group
consisting of chromium (Cr), silicon (Si), titanium (Ti), zirconium
(Zr), and silicon carbide (SiC).
8. The disc drive storage system of claim 7 wherein the adhesive
layer has a thickness in a range of about 1 nanometer to about 1
micrometer.
9. A motor, comprising: a housing having a central axis; a
stationary member that is fixed with respect to the housing and
coaxial with the central axis; a stator fixed with respect to the
housing; a rotatable member that is rotatable about the central
axis with respect to the stationary member; a rotor supported by
the rotatable member and magnetically coupled to the stator; and a
hydrodynamic bearing interconnecting the stationary member and the
rotatable member, the bearing having at least a portion of one
working surface comprising a tilt-limiting layer.
10. The motor of claim 9 wherein the tilt-limiting layer comprises
a material that improves the hardness of the working surface of the
bearing.
11. The motor of claim 9 wherein the tilt-limiting layer reduces
the coefficient of friction of the working surface of the
bearing.
12. The motor of claim 9 wherein the tilt-limiting layer comprises
a material selected from the group consisting of
diamond-like-carbon, hydrogenated diamond-like-carbon, nitrogenated
diamond-like-carbon, nickel phosphide (NiP), nickel boride (NiB),
and combinations thereof.
13. The motor of claim 9 wherein the tilt-limiting layer has a
thickness sufficient to limit tilting between the working surfaces
of the spindle motor.
14. The motor of claim 9 wherein the tilt-limiting layer is formed
on an adhesive layer.
15. The motor of claim 14 wherein the adhesive layer comprises one
or more material selected from the group consisting of chromium
(Cr), silicon (Si), titanium (Ti), zirconium (Zr), and silicon
carbide (SiC).
16. The motor of claim 14 wherein the adhesive layer has a
thickness in a range of about 1 nanometer to about 1
micrometer.
17. A motor, comprising: a hydrodynamic bearing interconnecting a
stationary member and a rotatable member, wherein the hydrodynamic
bearing has at least one working surface; and a portion of the at
least one working surface has a tilt-limiting means thereon.
18. The motor of claim 17 wherein the tilt-limiting means comprises
a material that improves the hardness of the working surface of the
bearing.
19. The motor of claim 17 wherein the tilt-limiting means reduces
the coefficient of friction of the working surface of the
bearing.
20. The motor of claim 17 wherein the tilt-limiting means has a
thickness sufficient to limit tilting between the working surfaces
of the hydrodynamic bearing.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. provisional patent
application serial No. 60/396,760, filed Jul. 17, 2002, which is
herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to the field of fluid dynamic
bearing assemblies of the type that cooperate with high-speed
spindle elements. More specifically, the invention relates to
restricting the tilting distance between rotating and stationary
members of bearing assemblies utilized in a disc drive system.
[0004] 2. Description of the Related Art
[0005] Disc drive memory systems have been used in computers for
many years for the storage of digital information. Digital
information is recorded on concentric memory tracks of a magnetic
disc medium in the form of magnetic transitions within the medium.
The discs themselves are rotatably mounted on a spindle. The
information is accessed by means of read/write heads generally
located on a pivoting arm that moves radially over the surface of
the disc. The read/write heads or transducers must be accurately
aligned with the storage tracks on the disc to ensure proper
reading and writing of information.
[0006] During operation, the discs are rotated at very high speeds
within an enclosed housing by means of an electric motor generally
located inside a hub that supports the discs. One type of motor in
common use is known as an in-hub or in-spindle motor. Such
in-spindle motors typically have a spindle mounted by means of two
ball or hydrodynamic bearing systems to a motor shaft disposed in
the center of the hub. Generally, such motors include a stator
comprising a plurality of teeth arranged in a circle. Each of the
teeth support a plurality of coils or windings that may be
sequentially energized to polarize the stator. A plurality of
permanent magnets are disposed in alternating polarity adjacent the
stators. As the coils disposed on the stators are sequentially
energized in alternating polarity, the magnetic attraction and
repulsion of each stator to the adjacent magnets cause the spindle
to rotate, thereby rotating the disc and passing the information
storage tracks beneath the head.
[0007] The use of hydrodynamic bearing assemblies in such drive
systems has become preferred due to desirable reductions in drive
size and noise generation as compared to conventional ball bearing
drive systems. In hydrodynamic bearings, a lubricating fluid, such
as oil or air, functions as the bearing surface between a
stationary base or housing and a rotating spindle or hub. The
lubricating fluid requires gaps between the stationary and rotating
members in order to provide the support, stiffness and lubricity
required for proper bearing operation.
[0008] These gaps between the stationary and rotating members of
the bearing may permit the rotating member to become tilted with
respect to the stationary member. This tilting of the rotating
member within the gaps may create contact points between the
rotating and stationary bearing members. Such contact points may
wear down the surfaces on both the rotating and stationary members
at the points of contact enlarging the gap therebetween and
undesirably affecting the performance of the bearing by creating
particles.
[0009] Therefore, there is a need in the art for restricting the
tilting distance between rotating and stationary members of bearing
assemblies utilized in disc drive systems.
SUMMARY OF THE INVENTION
[0010] The disc drive data storage system of the present invention
includes a hydrodynamic bearing comprising a housing having a
central axis, a stationary member that is fixed with respect to the
housing and coaxial with the central axis, and a rotatable member
that is rotatable about the central axis with respect to the
stationary member. A stator is fixed with respect to the housing. A
rotor is supported by the rotatable member and is magnetically
coupled to the stator. At least one data storage disc is attached
to and is coaxial with the rotatable member. At least a portion of
a surface of one or more of the hydrodynamic bearing components has
a tilt-limiting layer formed thereon to restrict the tilting
distance between the working surfaces in the disc drive data
storage system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] So that the manner in which the above recited features of
the present invention are attained and can be understood in detail,
a more particular description of the invention, briefly summarized
above, may be had by reference to the embodiments thereof which are
illustrated in the appended drawings.
[0012] It is to be noted, however, that the appended drawings
illustrate only typical embodiments of this invention and are
therefore not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
[0013] FIG. 1 is a top plan view of a disc drive data storage
device in accordance with the present invention;
[0014] FIG. 2 is a sectional view of a hydrodynamic bearing spindle
motor in accordance with the present invention;
[0015] FIG. 3 is a partial sectional view of one embodiment of a
hydrodynamic bearing including a tilt-limiting layer in accordance
with the invention; and
[0016] FIG. 4 is a partial sectional view of another embodiment of
a hydrodynamic bearing including a tilt-limiting layer in
accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] The present invention is a disc drive data storage device
including a hydrodynamic bearing having a tilt-limiting layer
thereon to restrict the tilting distance between the working
surfaces thereof. FIG. 1 is a plan view of a typical disc drive 10
wherein the present invention is useful. Disc drive 10 includes a
housing base 12 and a top cover 14. The housing base 12 is combined
with top cover 14 to form a sealed environment to protect the
internal components from contamination by elements from outside the
sealed environment.
[0018] The base and top cover arrangement shown in FIG. 1 is common
in the industry. However, other arrangements of the housing
components have been frequently used, and the invention is not
limited to the configuration of the disc drive housing shown in
FIG. 1. For example, disc drives have been manufactured using a
vertical split between two housing members. In such drives, that
portion of the housing half that connects to the lower end of the
spindle motor is analogous to base 12, while the opposite side of
the housing member, that is connected to or adjacent the top of the
spindle motor, is functionally the same as the top cover 14.
[0019] Disc drive 10 further includes a disc pack 16 that is
mounted for rotation on a spindle motor (not shown) by a disc clamp
18. Disc pack 16 includes a plurality of individual discs that are
mounted for co-rotation about a central axis. Each disc surface has
an associated head 20 that is mounted to disc drive 10 for
communicating with the disc surface. In the example shown in FIG.
1, heads 20 are supported by flexures 22 that are in turn attached
to head mounting arms 24 of an actuator body 26. The actuator shown
in FIG. 1 is of the type known as a rotary moving coil actuator and
includes a voice coil motor (VCM), shown generally at 28. Voice
coil motor 28 rotates actuator body 26 with its attached heads 20
about a pivot shaft 30 to position heads 20 over a desired data
track along an arcuate path 32. While a rotary actuator is shown in
FIG. 1, the invention is also useful in disc drives having other
types of actuators, such as linear actuators.
[0020] FIG. 2 is a sectional view of a hydrodynamic bearing spindle
motor 132 in one embodiment of the invention. Spindle motor 132
includes a stationary member (shaft) 134, a hub 136 and a stator
138. In the embodiment shown in FIG. 2, the shaft 134 is fixed and
attached to base 112 through a nut 140 and a washer 142.
[0021] The hub 136 is supported by the shaft 134 through a
hydrodynamic bearing 137 for rotation about shaft 134. The hub 136
includes a disc carrier member 166 that supports disc pack 16
(shown in FIG. 1) for rotation about shaft 134. The disc pack 16 is
held on disc carrier member 166 by the disc clamp 18 (also shown in
FIG. 1). A plurality of permanent magnets 170 are attached to the
outer diameter of the hub 136, with the hub 136 and magnets 170
acting as a rotor for the spindle motor 132.
[0022] The stator 138 is generally formed of a stack of stator
laminations 172 and associated stator windings 174. Each stator
lamination 172 comprises a plurality of teeth (not shown) that
extend toward a central axis 197. The plurality of phase windings
174 are wound on the stator teeth (not shown) for magnetic
communication with the rotor (i.e., magnets 170 and hub 136). The
stator windings 174 may have a number of winding configurations.
Some examples of phase windings that may benefit from the invention
are discussed in U.S. Pat. No. 5,579,188, entitled IRONLESS
HYDRODYNAMIC SPINDLE MOTOR, issued Nov. 26, 1996 to Dunfield et
al., and in U.S. Pat. No. 5,590,003, entitled HYDRODYNAMIC SPINDLE
MOTOR HAVING DISTRIBUTED WINDINGS, issued Dec. 31, 1996 to Dunfield
et al., both of which are commonly assigned and are hereby
incorporated by reference in their entirety.
[0023] The stator 138 is generally retained in the base 112 by
fasteners, adhesives, or other conventional methods. In the
illustrated embodiment, the stator 138 is disposed in a pocket
formed in the base 112. A tab 120 is fastened by a screw 122 to the
base 112 and includes a portion that overlies the stator 138 thus
retaining the stator 138 in the pocket of the base 112. The bearing
137 includes a radial working surface 146 and axial working
surfaces 148 and 150. The shaft 134 includes fluid ports 154, 156
and 158 that supply hydrodynamic fluid 160 and assist in
circulating the fluid along the working surfaces of the bearing.
Generally, the hydrodynamic fluid 160 is comprised of air, light
oil or other bearing lubricant.
[0024] In the embodiment shown in FIG. 2, spindle motor 132 is a
"below-hub" type motor in which stator 138 has an axial position
that is below hub 136. Stator 138 also has a radial position that
is external to hub 136, such that stator windings 174 are secured
to an inner surface (not shown) of stator laminations 172. In an
alternative embodiment, the stator is positioned within the hub, as
opposed to below the hub. The stator can have a radial position
that is either internal to the hub or external to the hub. In
addition, the spindle motor can have a fixed shaft, as shown in
FIG. 2, or a rotating shaft. In a rotating shaft spindle motor, the
bearing is located between the rotating shaft and an outer
stationary sleeve that is coaxial with the rotating shaft.
[0025] The spindle motor 132 further includes a thrust plate 145
that forms axial working surfaces 148 and 150 of hydrodynamic
bearing 137. A counter plate 162 cooperates with the working
surface 148 to provide axial stability for the hydrodynamic bearing
and to position the hub 136 within the spindle motor 132. An o-ring
164 is provided between the counter plate 162 and the hub 136 to
seal the hydrodynamic bearing 137. The o-ring 164 prevents
hydrodynamic fluid 160 from escaping between the counter plate 162
and the hub 136. If an o-ring is not used then the counter plate
may be welded to the hub in order to seal the hydrodynamic bearing.
Examples of hydrodynamic bearings that may benefit from the
invention are described in U.S. Pat. No. 5,993,066, entitled FLUID
RETENTION PRINCIPLE FOR HYDRODYNAMIC BEARINGS, issued Nov. 30, 1999
to Leuthold et al., U.S. Pat. No. 5,977,674, entitled SINGLE PLATE
HYDRODYNAMIC BEARING WITH SELF-BALANCING FLUID LEVEL, issued Nov.
2, 1999 to Leuthold et al., and U.S. Pat. No. 6,004,036, entitled
FLUID DYNAMIC BEARING CARTRIDGE DESIGN INCORPORATING A ROTATING
SHAFT, issued Dec. 21, 1999 to Kloeppel et al., all of which are
commonly assigned and are hereby incorporated by reference in their
entirety. The present invention is useful with this and other forms
of hydrodynamic bearings and is not limited to use with this
particular configuration.
[0026] In operation, the windings are energized, causing the hub
136 to rotate. Commutation pulses applied to stator windings 174
generate a rotating magnetic field that communicates with rotor
magnets 170 and cause hub 136 to rotate about central axis 197 on
bearing 137. The commutation pulses are timed,
polarization-selected DC current pulses that are directed to
sequentially selected stator windings to drive the rotor magnet and
control the speed.
[0027] The pressure created by the bearing causes the hydrodynamic
fluid 160 to flow out from the ports 154, 156 and 158 towards the
thrust plate 145. Generally, grooves (not shown) disposed in the
shaft 134 and/or thrust plate 145 pump the hydrodynamic fluid 160
respectively between the axial working surfaces 148, 150 and the
counter plate 162 and the hub 136. The pumping action builds up
multiple pressure zones along the bearing 137, maintaining a fluid
film between the rotating ports and providing stiffness to the
bearing 137.
[0028] To effectively pump and maintain the hydrodynamic fluid 160
in the desired locations within the bearing 137, gaps defined
between the working surface 148 and the counter plate 162 and the
working surfaces 146, 150 and the hub 136 must be set to a tightly
controlled distance. Typically, the distance or clearance of the
gap is set between about 2 .mu.m (micrometers) and about 50 .mu.m,
dependant on the motor size, hydrodynamic fluid used and
operational speed. Design tolerance of the gap to ensure the
desired performance is typically plus or minus 1 .mu.m.
[0029] As described above, "tilting" of the rotating member within
the gaps between the working surfaces of the hydrodynamic bearing
137 can result in failure of the disk drive 10. Tilting may create
contact points between the rotating and stationary bearing members.
Tilting can occur between the following surfaces: working surface
150 between the thrust plate 145 and the hub 136, working surface
148 between the thrust plate 145 and counter plate 162, as well as
working surfaces 146 between the shaft 134 and the hub 136. If
tilting occurs, the hydrodynamic bearing 137 can fail resulting in
catastrophic failure of the disc drive system.
[0030] Referring to FIGS. 3-4 at least a portion of one of the
working surfaces (radial working surfaces 146 and the axial working
surfaces 148 and 150) defined by the counter plate 162, the thrust
bearing 145, the shaft 134 and the hub 136 have a tilt-limiting
layer 200 formed thereon. The tilt-limiting layer 200 functions to
restrict the tilting distance between the working surfaces in the
disc drive data storage system.
[0031] The tilt-limiting layer 200 is preferably formed in the
locations of maximum rotation as well as areas where point contacts
occur. In FIG. 3, for example, the tilt-limiting layer 200 is
provided on working surface 146 at one or more ends of shaft 134.
The tilt-limiting layer 200 reduces rotational tilt by reducing the
gap between the rotating and stationary bearing members.
Alternatively, in FIG. 4, the tilt limiting layer 200 may be
provided on other working surfaces of the spindle motor, such as,
for example, axial working surface 150 on the hub 136.
[0032] The tilt-limiting layer 200 may comprise one or more
coatings of a material that improves the hardness and/or reduces
the coefficient of friction of the working surfaces of the spindle
motor. Suitable materials may include, for example,
diamond-like-carbon, hydrogenated diamond-like-carbon, nitrogenated
diamond-like-carbon, nickel phosphide (NiP), nickel boride (NiB),
or combinations thereof, among other materials.
[0033] The tilt-limiting layer 200 may have a thickness sufficient
to limit the tilting between the working surfaces of the spindle
motor. For example, the tilt-limiting layer may typically have a
thickness in the range of about 1 .mu.m (micrometer) to about 3
.mu.m. However, the preferred thickness for the tilt-limiting layer
200 is dependent upon factors such as the composition of the outer
diameter of shaft 134, the magnitude of the gap between, for
example, the shaft 134 and the hub 136, surface roughness and
loading, among others.
[0034] In one embodiment, the tilt-limiting layer 200 may be
deposited by physical vapor deposition (PVD), such as by a
sputtering process. In another embodiment, the tilt-limiting layer
200 may be deposited by chemical vapor deposition (CVD), such as
plasma enhanced chemical vapor deposition (PECVD). In another
embodiment, the tilt-limiting layer 200 may be deposited by ion
beam deposition. The tilt-limiting layer 200 may also be sputtered
in the presence of, for example, hydrogen (H.sub.2) or nitrogen
(N.sub.2) to enhance the frictional properties thereof.
[0035] While FIGS. 3-4 depict the tilt-limiting layer 200 as
consisting of only one layer, it is within the scope of the
invention for the tilt-limiting layer 200 to consist of multiple
coating layers. It is often desirable for tilt-limiting layers 200
to consist of multiple layers in order to provide optimal adhesion,
reduce crack propagation and to improve corrosion resistance of the
shaft 134. In one embodiment, the tilt-limiting layer 200 may
comprise two or more layers of diamond-like-carbon.
[0036] In one embodiment, one or more adhesive layers 201 (FIG. 4)
may be deposited on portions of working surface 150 prior to
depositing the tilt-limiting layer 200. The adhesive layers 201
provide improved adhesion and mechanical properties for the
tilt-limiting layers to the hub 136. The adhesive layers 201 may
comprise, for example, chromium (Cr), silicon (Si), titanium (Ti),
zirconium (Zr), silicon carbide (SiC), as well as combinations
thereof.
[0037] The thickness of the adhesive layers 201 may be in the range
of about 1 nm (nanometer) to about 1 .mu.m. The preferred thickness
of the adhesive layers 201 is dependent upon factors similar to
those enumerated above for tilt-limiting layer 200.
[0038] In one embodiment, the adhesive layers 201 are deposited by
physical vapor deposition (PVD), such as by a sputtering process.
In another embodiment, the adhesive layers 201 are deposited by
chemical vapor deposition (CVD), such as plasma enhanced chemical
vapor deposition (PECVD). In another embodiment, the adhesive
layers 201 are deposited by ion beam deposition.
[0039] In one embodiment, the shaft 134 may be etched prior to
depositing the adhesive and tilt-limiting layers. In the case where
no adhesive layer is deposited, the shaft 134 may be etched prior
to depositing the tilt-limiting layer. The shaft 134 may be etched,
for example, by a plasma etching process. The plasma etching
process may comprise bombarding the substrate with ions of an inert
gas such as, for example, argon (Ar).
EXAMPLE 1
[0040] A tilt-limiting layer was deposited on a steel shaft of a
spindle motor. The tilt-limiting layer comprised
diamond-like-carbon. The tilt-limiting layer was deposited by a
sputtering process, in which an inert gas sputtered material from a
diamond-like-carbon target. A tilt-limiting layer having a
thickness of about 1.2 .mu.m to about 1.4 .mu.m was deposited.
[0041] While foregoing is directed to the preferred embodiment of
the present invention, other and further embodiments of the
invention may be devised without departing from the basic scope
thereof, and the scope thereof is determined by the claims that
follow.
* * * * *